Seal coats to prevent silicon loss during re-melt infiltration of Si containing composites

ABSTRACT

Provided is a method including obtaining ceramic matrix composite (CMC) with a first matrix portion including a silicon carbide and silicon phase dispersed therewithin, disposing a coating thereupon to form a sealed part, and forming thereupon another segment comprising a CMC, which may be another matrix portion including a silicon carbide and a silicon phase dispersed within therewithin. Also provided is a gas turbine component with a CMC segment including a matrix portion including a silicon carbide and a silicon phase dispersed therewithin, a sealing layer including silicon carbide enclosing the first segment, and a second segment on the sealing layer, wherein the second segment includes a melt-infiltrated CMC having a matrix portion including a silicon carbide and a silicon phase dispersed therewithin.

FIELD

The invention relates generally to sealing a ceramic matrix composite(CMC) part to prevent loss of silicon from the part during subsequentformation of another CMC segment upon it.

BACKGROUND

Ceramic matrix composites (CMCs), including CMCs that are reinforcedwith fibers, were developed to alleviate damage tolerance issues ofmonolithic ceramics such as SiC ceramics and have become attractive forhigh temperature structural applications, such as in gas turbineengines. One type of fiber-reinforced CMCs that is particularlyattractive for high temperature structural applications is reactive meltinfiltrated fiber-reinforced CMCs (hereinafter “MI-CMCs”).

In MI-CMCs, a preform of fibers and matrix constituents is infiltratedwith a metal which produces a ceramic matrix when reacting with thematrix constituents. SiC-based MI-CMCs, wherein the infiltrating metalis silicon or a silicon alloy and the matrix constituents are such thatthe resulting matrix is substantially SiC (e.g., SiC and/or Cparticulates), are particularly attractive for high temperaturestructural applications because of their high thermal conductivity,excellent thermal shock resistance, creep resistance, and oxidationresistance compared to other CMCs.

In gas turbine applications MI-CMC components are often subjected toloads above the matrix cracking stress of the components. The resultingcracks in the matrix portion of the components from such stresses act todecrease the stiffness and oxidation resistance of the MI-CMC composite,and can lead to premature failure of the MI-CMC component. Further,temporary overstress conditions, such as from dropped parts or tools,can occur during MI-CMC component fabrication, transportation and/orinstallation and also can result in matrix cracks. General wear may alsoshorten the lifespan of MI-CMC components. Effective methods of repairare therefore needed, so that MI-CMC components that exhibit cracks orother damage can be returned to a suitable state for use rather thanneeding to be replaced.

One option for repairing MI-CMC components is to fill cracks orrefurbish other worn or damaged aspects by performing a MI process onthe damaged MI-CMC component. However, an undesirable consequence ofsuch a repair process may be that material such as Si gets lost fromoriginal portions of the MI-CMC component, such as by volatizationduring an MI process or seepage of silicon into capillaries of anadditional MI-CMC segment added to the component being reworked. Thus, aneed exists for methods and related configurations, components andassemblies for repairing matrix cracks in MI-CMC components to restorethem to a usable condition without loss of Si or other material duringrepair.

SUMMARY

In one aspect, provided is a method of obtaining a part including afirst ceramic matrix composite (CMC) with a first matrix portion whereinthe first matrix portion includes a first silicon carbide and a firstsilicon phase dispersed within the first silicon carbide, sealing thepart wherein sealing includes disposing a coating on the part to form asealed part, and forming on the sealed part a segment comprising asecond CMC. In some embodiments, the second CMC may be a second matrixportion including a second silicon carbide and a second silicon phasedispersed within the second silicon carbide.

In another aspect, provided is a method of obtaining a part including afirst ceramic matrix composite (CMC) including a first matrix portionwherein the first matrix portion includes a first silicon carbide and afirst silicon phase dispersed within the first silicon carbide, sealingthe part including disposing a coating on the part to form a sealedpart, where disposing includes performing chemical vapor deposition, andthe coating includes silicon carbide, forming on the sealed part asegment comprising a second CMC having a second matrix portion includinga second silicon carbide and a second silicon phase dispersed within thesilicon carbide, and forming includes performing melt infiltration.

In a further aspect, provided is a gas turbine component with a firstsegment including a ceramic matrix composite (CMC) including a firstmatrix portion wherein the first matrix portion includes a first siliconcarbide and a first silicon phase dispersed within the silicon carbide,a sealing layer including silicon carbide wherein the sealing layerencloses the first segment and comprises an external surface, and asecond segment on the external surface of the sealing layer, wherein thesecond segment includes a melt-infiltrated CMC having a second matrixportion and the second matrix portion includes a second silicon carbideand a second silicon phase dispersed within the silicon carbide.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings,wherein:

FIG. 1 is a flow-chart illustrating one example of a method for sealinga CMC part and forming a second CMC on the sealed part.

FIG. 2A is an illustration of a CMC component part of gas turbineengine, FIG. 2B is an illustration of a CMC component part of gasturbine engine on which a coating has been disposed to seal the part,and FIG. 2C is an illustration of a CMC component part of gas turbineengine on which a coating has been disposed to seal the part with asecond CMC on the external surface of the sealing part.

DETAILED DESCRIPTION

Each embodiment presented below facilitates the explanation of certainaspects of the disclosure, and should not be interpreted as limiting thescope of the disclosure. Moreover, approximating language, as usedherein throughout the specification and claims, may be applied to modifyany quantitative representation that could permissibly vary withoutresulting in a change in the basic function to which it is related.Accordingly, a value modified by a term or terms, such as “about,” isnot limited to the precise value specified. In some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. When introducing elements of variousembodiments, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements. As usedherein, the terms “may” and “may be” indicate a possibility of anoccurrence within a set of circumstances; a possession of a specifiedproperty, characteristic or function; and/or qualify another verb byexpressing one or more of an ability, capability, or possibilityassociated with the qualified verb. Accordingly, usage of “may” and “maybe” indicates that a modified term is apparently appropriate, capable,or suitable for an indicated capacity, function, or usage, while takinginto account that in some circumstances, the modified term may sometimesnot be appropriate, capable, or suitable. Any examples of operatingparameters are not exclusive of other parameters of the disclosedembodiments. Components, aspects, features, configurations,arrangements, uses and the like described, illustrated or otherwisedisclosed herein with respect to any particular embodiment may similarlybe applied to any other embodiment disclosed herein.

In one aspect, an embodiment of the present invention includes a methodof repairing a CMC component part by an MI process, where the CMCcomponent includes a first matrix portion having a first silicon carbideand a first silicon phase dispersed within the first silicon carbide,sealing the part by disposing a coating on the part to form a sealedpart, and forming a segment including a second CMC on the sealed part. Asilicon phase is defined herein as containing substantially elementalsilicon with any other elements, such as boron, dissolved in the siliconphase. In some embodiments, the second CMC includes a second matrixportion with a second silicon carbide and a second silicon phasedispersed within the second silicon carbide. In some embodiments, thecoating may be disposed by a chemical vapor deposition (CVD) process. Insome embodiments, the coating may include silicon carbide or siliconnitride. The CMC component part may be a gas turbine part, such as butnot limited to a blade, a vane, a nozzle, a shroud, a combustor liner,or a center frame. In some embodiments, the part may be a component inneed of repair, and sealing the part by forming a sealing portion orcoating on the part is performed during repair of the part.

Forming a second CMC may include performing an MI process to form asecond CMC on the sealed part. In some embodiments, a second siliconcarbide is melt-infiltrated with a second silicon phase, withmelt-infiltrating including disposing silicon on the second siliconcarbide, heating the silicon disposed on the second silicon carbide to afirst temperature equal to or greater than a melting point of thesilicon disposed on the second silicon carbide to form molten silicondisposed on the second silicon carbide, controlling the atmosphere aboutthe part while heating the silicon disposed on the second siliconcarbide to the first temperature, allowing the molten silicon disposedon the second silicon carbide to infiltrate the second silicon carbide,and cooling the part to a second temperature that is below the meltingpoint of the silicon that infiltrated the second silicon carbide to formthe second silicon phase. For example, the first temperature may bebetween about 1300° C. and 1600° C., such as between about 1380° C. and1500° C.

In some embodiments, a second silicon carbide is melt-infiltrated with asecond silicon phase, including contacting the second silicon carbidewith a wick, wetting the wick with molten silicon at a first temperatureequal to or greater than a melting point of silicon, controlling theatmosphere about the part while contacting the second silicon carbidewith the wick, infiltrating the second silicon carbide with the moltensilicon wherein infiltrating comprises wicking the molten silicon fromthe wick, and cooling the part to a second temperature that is below themelting point of the silicon that infiltrated the second silicon carbidethe to form the second silicon phase.

In another aspect, a gas turbine component has a first segment includinga CMC, with a first matrix portion including a first silicon carbide anda first silicon phase dispersed within the first silicon carbide, asilicon carbide sealing layer enclosing the first segment and with anexternal surface, and a second segment of the external surface of thesealing layer with melt-infiltrated CMC having a second matrix portionwith a second silicon carbide and a second silicon phase dispersedwithin the second silicon carbide. Nonlimiting examples of a gas turbinecomponent include a blade, a vane, a nozzle, a shroud, a combustorliner, and a center frame. A gas turbine may include such a gas turbinecomponent, in accordance with the present disclosure.

In one aspect, a coating deposited on a part to seal the part includesdepositing on the part a substance or material with a coefficient ofthermal expansion similar to that of the part itself. Substantialdifferences in coefficients of thermal expansion between a CMC componenton which a sealing coating is deposited and material of which a coatingis made may result in formation of cracks or fissures during subsequentprocessing steps and/or use of a component following processing. Forexample, a CMC may include silicon or a silicon alloy, and may alsocontain silicon carbide. Examples of materials that may be used forforming a sealing layer on such a CMC include silicon carbide, siliconnitride, and boron carbide.

Various methods known to skilled artisans may be employed to deposit asealing coating on a CMC part. Any method suitable for depositing acoating with sufficient compatibility and desirable thermal expansionparameters, in view of the composition of the CMC part, may be adoptedfor such use. A sealing coating is formed to seal in silicon-containingcomponents in the CMC during refurbishing, repair, restructuring, andthe like, which may include a subsequent MI step. When an MI step isperformed to restructure, repair, rebuild, densify, strengthen, enlarge,or otherwise modify a CMC, such as a CMC component which was itselfformed by an MI process, a temperature above the melting point ofsilicon may be applied. Conventionally, if residual silicon present inthe CMC has access to the ambient or furnace environment during suchheating, it may evaporate and be lost from the CMC component, resultingin gaps, voids, pockets, or fissures in the CMC component. Also, whenreworking or refurbishment entails addition of further CMC segments suchas by an MI process, silicon present in the original body of the CMCcomponent may melt at the higher temperatures the component is exposedto during MI and the melted silicon may be pulled into fine capillariesof the added, newly formed “green” CMC material by capillary action.Upon cooling, such silicon may remain in the green CMC portion, leavingvoids, fissures, cracks, pores, or other undesirable elements in theoriginal CMC component body.

Applying a sealing coating to the initial CMC component, in accordancewith the present invention, separates silicon within the original CMCcomponent from the ambient environment and the green CMC material thatmay be subsequently deposited during heating, such as during an MIprocess. Under such circumstances, although the CMC with a sealingcoating may be exposed to a temperature above, for example, a meltingpoint of silicon, loss of silicon from the CMC component and formationof faults therein would be reduced, minimized, or eliminated, because asealing coating would prevent access of volatized silicon, andsubsequent loss, to the environment or capillaries of the green CMCsegment.

Conventional methods known to those skilled in the art may be used todeposit a sealing coating layer. Such conventional methods may generallyinclude, but should not be limited to, chemical vapor deposition (CVD),chemical vapor infiltration, plasma spraying, high velocity plasmaspraying, low pressure plasma spraying, solution plasma spraying,suspension plasma spraying, high velocity oxygen flame (HVOF), electronbeam physical vapor deposition (EBPVD), sol-gel, sputtering, slurryprocesses such as dipping, spraying, tape-casting, rolling, andpainting, and combinations of these methods. In a preferred embodiment,a sealing coating layer may be deposited by CVD.

In some embodiments, deposition of a sealing coating layer may includereacting a surface of the CMC component with a compound or chemical. Forexample, silicon present at or near surfaces of the CMC component may beavailable for chemical; reactivity with other compounds, presented undersuitable conditions. Upon exposure to such compounds under suchconditions, such surface-available silicon may react with such compoundsor substances to result in the formation of a sealing coating layer atand around the surface of the CMC component, thereby separating siliconon the interior of the CMC component from the ambient environment toprevent subsequent silicon loss due to volatization. For example,methods well known to skilled artisans for carburizing or nitridingsurfaces, by exposing a CMC component to carbon or nitrogen underconditions of high heat, may be used to react surface silicon in the CMCcomponent with carbon or nitrogen to form a carburized or nitridedsurface. Optionally, subsequent heat treatment may also be applied.Reacting surface silicon in the CMC component with carbon or nitrogenmay result in the formation of a sealing coating to prevent loss ofinterior silicon due to vaporization.

Once a sealing coating has been formed on a surface of a CMC component,additional material may be added to the CMC component, such as forrefurbishment, repair, or other modification that includes addition ofadditional structure to the component. For example, a further segmentmay be an MI-CMC component. Formation of such additional MI-CMCcomponent may be achieved by any of a variety of methods known toskilled artisans. Nonlimiting examples include processes known as a“prepreg process” and another known as a “slurry cast” process.Processes may differ in how a green composite preform is formed, but indifferent embodiments a final densification step may involve a siliconmelt infiltration step into the green composite preforms for the addedMI-CMC segment.

Once a green body composite preform containing the fibers and matrixconstituents is formed, it is heated while in contact with a source ofsilicon metal or alloy which produces a ceramic matrix when reactingwith the matrix constituents. The molten infiltrating silicon phasereadily wets the matrix constituents (e.g., SiC and/or carbon matrixconstituents) of the green body composite preform, and therefore iseasily pulled into a portion of the porosity of the preform by capillaryaction. No external driving force is typically needed for theinfiltration of silicon into the matrix constituents and there istypically no dimensional change of the composite preform as a result ofthe infiltration (as the porosity of the preform is filled withsilicon). Current conventional processes for melt infiltration offiber-reinforced CMCs using silicon (e.g., silicon metal or alloy)utilize batch processes where either silicon metal powder is appliedonto the surface of the preform, or silicon is transferred to thepreform in the molten state using a porous carbon wick.

Conventionally, performing such steps may result in loss of siliconphase from the original CMC component body. In accordance with thepresent invention, sealing the original CMC component with a sealinglayer prevents such loss and resultant formation of faults within theoriginal CMC component segment. Thus, silicon may be added duringdensification of the newly formed CMC component during an MI step byadding exogenous silicon, not by siphoning silicon off of the originalCMC component, which retains its silicon phase.

Upon infiltration of molten silicon, such as via capillary action duringthe silicon infiltration processes discussed above, the silicon is drawninto some of the porosity of the matrix constituents of the newly formedCMC and may react with carbon thereof to form a SiC-based MI-CMCcomponent with a matrix portion including a substantially SiCcrystalline structure about the fibers (e.g., SiC fibers). In additionto forming a ceramic SiC crystalline structure of a matrix portion, thesilicon infiltration process fills at least some of the remainingporosity of the matrix portion with silicon metal or alloy that does notreact with carbon of the constituents. In this way, interconnectedpockets of “free” or un-reacted silicon phase may be formed within thematrix portion. In this way, a matrix portion of some exemplarySiC-based, newly added MI-CMC segments may be a substantially Si—SiCmatrix portion. In some embodiments, infiltrated “free” silicon phase insuch matrix portion (i.e., Si that does not form SiC) may be about 2 vol% to about 50 vol % of a matrix portion, and more preferably about 5 vol% to about 35 vol % of a matrix portion, and even more preferably about7 vol % to about 20 vol % of a matrix portion.

Silicon may be disposed on the matrix portion of a newly added MI-CMCcomponent, which itself is formed on a sealed coated original CMCcomponent, then exposed to a temperature above the melting point ofsilicon, forming molten silicon. Molten silicon is then allowed todisperse into the matrix portion of the added MI-CMC segment. In anotherembodiment, silicon may be contacted to a wick then exposed to atemperature above the melting point of silicon to form molten silicon,which, by capillary action, may be drawn into the matrix portion of thenewly added MI-CMC component segment, itself formed upon the sealedcoated original CMC component segment. Molten silicon may be formed byexposing silicon on the newly formed matrix portion, MI-CMC segment, orwick contacting the silicon to such segment, to a temperature of between1300° C. and 1600° C. For example, a temperature of between 1380° C. and1500° C. may be attained. Temperatures outside these ranges may also beused. When it is no longer desirable or needed for silicon to remain ina molten form, the temperature may be lowered to a temperature below themelting point of silicon to permit it to solidify, such as distributedamong and within matrix components of the newly formed MI

In some embodiments, densifying the newly formed MI-CMC may includecontrolling the atmosphere about such component while it is heated. Insome embodiments controlling the atmosphere about the component whilethe component is heated may include heating the component in a vacuumfurnace. In some such exemplary embodiments, the vacuum furnace may beconfigured to heat the component in a non-oxidizing atmosphere (i.e. theresidual gases within the furnace have no significantly deleteriouseffect on the infiltrating silicon). In some embodiments the furnace maybe configured to heat the component in an inert gas atmosphere. In someembodiments the furnace may be configured to heat the component in avacuum to substantially remove gas that is trapped or formed within thenewly formed MI-CMC component. For example, in some embodiments thefurnace may be configured to heat the component in a vacuum within therange of about 0.01 torr to about 2 torr, and preferably within therange of about 0.1 torr to about 1 torr.

An embodiment of a process of the present disclosure is illustrated inFIG. 1. Shown is a process 100 involving addition of a second CMCsegment to an original CMC part or component after the original CMC parthas been coated with a sealing portion or layer. In this embodiment, aCMC part or component is obtained 110. Optionally, the part or componentmay be in need of repair or refurbishment. It may have been damagedduring use, such as by the wearing away or breakage of a portion orportions or by formation of cracks or fissures. Some repairs may beeffectuated by incorporating additional silicon phase within the part,such as by an MI process, before additional structure is added to theCMC component, in accordance with known methods.

Subsequently, a surface of the original CMC component may be sealed byapplication of a coating layer 120. As described above, a coating layermay be selected to possess a coefficient of thermal expansionsubstantially similar to that of the original CMC component. A sealingcoating may comprise silicon carbide, silicon nitride, or boron carbide,or another material, or may be formed by carburization or nitriding ofthe surface of the CMC component. The sealing coating may be totallynonporous so as to form a complete barrier between silicon of thesilicon phase of the original CMC component. Optionally, in someembodiments, a sealing coating layer may be formed on only a portion ofthe CMC component, such as to form a barrier between the silicon of thesilicon phase of the original CMC and an MI-CMC formed on the other sideof the sealing coating layer from the original CMC component which doesnot otherwise contact the original CMC component or layer thereupon. Inthis manner, wicking of silicon phase from the original CMC componentinto a newly formed MI-CMC component segment may be prevented, withoutrequiring total sealing of the original CMC component. In otherembodiments, a sealing coating layer may be substantially total orcomplete around all surfaces of the original CMC component, yet possesssome porosity, while still retaining the ability to prevent, minimize,or reduce loss of silicon phase from the original CMC component due tovolatization during subsequent heating steps, such as during MIprocessing.

After formation of a sealing coating layer, a further CMC component maybe formed 130 as described above. The coefficient of thermal expansionof the sealing coating layer may be substantially similar to that of theCMC component segment added during this step. The added CMC componentsegment is formed on a surface of the sealing coating layer oppositefrom that which contacts the original CMC component. In this way, theadded CMC component may be considered to be external to the original CMCcomponent, as opposed to matrix or silicon phase of the original CMCcomponent, which may be considered to be internal to the original CMCcomponent.

An embodiment of a component formed during such processing isillustrated in FIG. 2A, FIG. 2B, and FIG. 2C. Shown in FIG. 2A is a CMCcomponent 210 in an initial state 200 such as if it is in need ofrepair, refurbishment, or reworking. In FIG. 2B, shown is a CMCcomponent 210 upon which a sealing coating layer 230 has been deposited,representing a state of the component part-way through the process 220.In FIG. 2C, shown is the addition of a second, newly formed CMCcomponent 250, such as by an MI process, as repair, refurbishment, orremodeling of the component continues 240. Different portions, segments,or layers are shown for exemplary illustrative purposes and are not toscale. Any CMC component may be represented by the forms illustrated inFIGS. 2A-2C, including a gas turbine component such as a blade, a vane,a nozzle, a shroud, a combustor liner, and a center frame, or anothercomponent. Any of the foregoing components may be assembled into andrendered part of a gas turbine in accordance with the presentdisclosure.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Numerous changes and modificationsmay be made herein by one of ordinary skill in the art without departingfrom the general spirit and scope of the invention as defined by thefollowing claims and the equivalents thereof. For example, theabove-described embodiments (and/or aspects thereof) may be used incombination with each other. In addition, many modifications may be madeto adapt a particular situation or material to the teachings of thevarious embodiments without departing from their scope. While thedimensions and types of materials described herein are intended todefine the parameters of the various embodiments, they are by no meanslimiting and are merely exemplary. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the various embodiments should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. Also, theterm “operably” in conjunction with terms such as coupled, connected,joined, sealed or the like is used herein to refer to both connectionsresulting from separate, distinct components being directly orindirectly coupled and components being integrally formed (i.e.,one-piece, integral or monolithic). Further, the limitations of thefollowing claims are not written in means-plus-function format and arenot intended to be interpreted based on 35 U.S.C. § 112, sixthparagraph, unless and until such claim limitations expressly use thephrase “means for” followed by a statement of function void of furtherstructure. It is to be understood that not necessarily all such objectsor advantages described above may be achieved in accordance with anyparticular embodiment. Thus, for example, those skilled in the art willrecognize that the systems and techniques described herein may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the disclosuremay include only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A method comprising: sealing a part, wherein thepart comprises a first ceramic matrix composite (CMC) including a firstmatrix portion, wherein the first matrix portion comprises a firstsilicon carbide and a first silicon phase dispersed within the firstsilicon carbide, and sealing comprises disposing a coating on a surfaceof the part to form a sealed part, wherein the coating is configured tominimize wicking of the first silicon phase, and forming on the sealedpart a segment comprising a second CMC.
 2. The method of claim 1,wherein the coating comprises silicon carbide.
 3. The method of claim 1,wherein disposing comprises depositing silicon carbide as the coating onthe surface of the part using chemical vapor deposition.
 4. The methodof claim 1, wherein the segment comprising the second CMC includes asecond matrix portion, wherein the second matrix portion comprises asecond silicon carbide and a second silicon phase dispersed within thesecond silicon carbide.
 5. The method of claim 4, wherein formingcomprises melt-infiltrating the second silicon carbide with the secondsilicon phase, and wherein melt-infiltrating comprises: disposingsilicon on the second silicon carbide, heating the silicon disposed onthe second silicon carbide to a first temperature equal to or greaterthan a melting point of the silicon disposed on the second siliconcarbide to form molten silicon disposed on the second silicon carbide,controlling the atmosphere about the part while heating the silicondisposed on the second silicon carbide to the first temperature,allowing the molten silicon disposed on the second silicon carbide toinfiltrate the second silicon carbide, and cooling the part to a secondtemperature that is below the melting point of the silicon thatinfiltrated the second silicon carbide to form the second silicon phase.6. The method of claim 5, wherein the first temperature is between about1300° C. and 1600° C.
 7. The method of claim 6, wherein the firsttemperature is between about 1380° C. and 1500° C.
 8. The method ofclaim 4, wherein forming comprises melt-infiltrating the second siliconcarbide with the second silicon phase, and wherein melt-infiltratingcomprises: contacting the second silicon carbide with a wick, wettingthe wick with molten silicon at a first temperature equal to or greaterthan a melting point of silicon, controlling the atmosphere about thepart while contacting the second silicon carbide with the wick,infiltrating the second silicon carbide with the molten silicon whereininfiltrating comprises wicking the molten silicon from the wick, andcooling the part to a second temperature that is below the melting pointof the silicon that infiltrated the second silicon carbide to form thesecond silicon phase.
 9. The method of claim 8, wherein the firsttemperature is between about 1380° C. and 1500° C.
 10. The method ofclaim 1, wherein the part is a gas turbine part.
 11. The method of claim10, wherein the part is selected from the group consisting of a blade, avane, a nozzle, a shroud, a combustor liner, and a center frame.
 12. Themethod of claim 1, wherein the part is a component in need of repair andsealing and forming comprise repairing the component.
 13. The method ofclaim 1, wherein forming comprises performing melt-infiltration.
 14. Themethod of claim 13, wherein the part is a gas turbine part selected fromthe group consisting of a blade, a vane, a nozzle, a shroud, a combustorliner, and a center frame.
 15. The method of claim 1, wherein thecoating has a thermal expansion coefficient that is substantiallysimilar to the thermal expansion coefficient of the first CMC.
 16. Themethod of claim 1, wherein the coating is non-porous.
 17. The method ofclaim 1, wherein sealing comprises disposing the coating on all surfacesof the part to form the sealed part.
 18. A method comprising: sealing apart, wherein the part comprises a first ceramic matrix composite (CMC)including a first matrix portion, wherein the first matrix portioncomprises a first silicon carbide and a first silicon phase dispersedwithin the first silicon carbide, and sealing comprises disposing acoating on a surface of the part to form a sealed part, disposingcomprises performing chemical vapor deposition, and the coatingcomprises silicon carbide, and wherein the coating is configured tominimize wicking of the first silicon phase; forming, on the sealedpart, a segment comprising a second CMC having a second matrix portion,wherein the second matrix portion comprises a second silicon carbide anda second silicon phase dispersed within the silicon carbide, and whereinforming comprises performing melt infiltration.
 19. The method of claim18, wherein the part is a gas turbine part selected from the groupconsisting of a blade, a vane, a nozzle, a shroud, a combustor liner,and a center frame.